Phlox is a family of colorful perennials. Tall garden phlox (Phlox paniculata) grows 1.5 to 5 feet tall and starts blooming around mid-June for a month or more, according to Iowa State University Extension. Low types such as moss, creeping and woodland phlox are used as spring groundcovers. The main challenge is powdery mildew on garden phlox, which you can reduce with spacing and resistant varieties.
Garden Phlox at a glance
| Type | Flower |
|---|---|
| Season | Perennial |
| Sun | Full sun |
| Plant spacing | 24 in |
| Row spacing | 24 in |
| Per square foot | 1 |
| Seed depth | At surface |
| Days to maturity | Blooms from mid-June for a month or more |
| How to start | Iowa State suggests dividing garden phlox in spring when new growth begins, or in late summer and early fall from mid-August through September. |
| Water | 1 in per week |
These are the same numbers our plant spacing, square foot and harvest date calculators use. See every crop in the plant database.
When to plant phlox
Iowa State suggests dividing garden phlox in spring when new growth begins, or in late summer and early fall from mid-August through September. Check your growing zone and frost dates.
How to plant phlox
- Pick a sunny spot. Garden phlox prefers sun and tolerates part sun.
- Use moist, well-drained soil with good air circulation.
- Leave room. Crowding promotes powdery mildew; use the plant spacing calculator.
- Water in hot, dry spells. See the garden watering calculator.
Caring for phlox
Water during hot, dry periods. Remove infected debris in fall. Late-summer divisions should be kept well watered and mulched 4 to 6 inches in November; remove the mulch in early March, per Iowa State.
Other types: woodland phlox (12 to 15 inches, partial shade, April to June, favored by rabbits), moss phlox (4 to 6 inches, sun, shear after flowering) and creeping phlox (6 to 12 inches, partial shade).
Companion plants
| Grow nearby | Coneflowers, daylilies, black-eyed Susans and ornamental grasses |
|---|---|
| Keep apart | Crowded, airless spots that encourage mildew |
Spotted phlox (<em>P. maculata</em>) blooms earlier than garden phlox and has better mildew resistance. Check other pairings with the companion plant finder.
Common problems
| Problem | What you see | What to do |
|---|---|---|
| Powdery mildew | Grayish-white coating on stems and leaves; leaves yellow and brown | Iowa State recommends adequate spacing, removing infected debris in fall and choosing resistant cultivars such as 'Frosted Elegance', 'Forever Pink', 'Bill Baker', 'Morris Berd' and 'Kim'. See the pest identifier. |
| Rabbit damage | Chewed young plants | Rabbits favor woodland phlox; fence new plants. |
| Yellow leaves | Leaves yellowing in dry spells | Water during hot, dry periods. See the yellow leaf identifier. |
Not sure what you are looking at? The plant problem identifier ranks likely causes from the symptoms you see.
When and how to harvest
Phlox is grown for its flowers. Make more plants by dividing clumps in spring or late summer.
Plan your phlox
- Plant spacing calculator: how many plants fit your bed
- Planting calendar: sowing and transplant dates for your frost dates
- Frost dates by ZIP code: your last spring and first fall frost
- Harvest date calculator: when your crop will be ready
Frequently asked questions
How far apart should I plant phlox?
Space phlox 24 inches apart in rows 24 inches apart. In a square foot garden, plant 1 per square foot.
How deep do I plant phlox plants?
Plant garden phlox at the same depth it grew in its pot, in moist, well-drained soil with room for air to move.
How long does phlox take to grow?
Garden phlox starts blooming around mid-June and lasts a month or more.
How much water does phlox need?
About 1 inch of water a week, from rain and watering combined. Water during hot, dry periods.
How do I prevent powdery mildew on phlox?
Give plants adequate space, remove infected debris in fall and choose resistant cultivars.
When should I divide phlox?
In spring when new growth begins, or from mid-August through September.
Which phlox are low growing?
Moss phlox (4 to 6 inches), creeping phlox (6 to 12 inches) and woodland phlox (12 to 15 inches).